1. Field of the Invention
The present invention is related to a hydraulic squeezing and shrinking machine for forming ends of a roller and particularly to a concentric machining device for ends of a roller.
2. Brief Description of Related Art
Referring to FIG. 1, a conventional machining and forming device for a roller usually provides a cylindrical blank roller 10 with a sufficient thickness available for being cut and worked. Then, the blank roller 10 is worked to provide a smooth outer surface with two conical ends 11 for a transmission belt such as a pedaling belt of a running machine moving on the roller 10 steadily without deviating leftward or rightward. The conical ends 11 are made a concentric bore as a journal 12 respectively with a lathe machine for a bearing 13 being mounted to the journal 12 such that the roller 10 is capable of turning smoothly. A spindle 14 is arranged in the center of the roller 10 to fit with the bearing 13 and is rotationally joined to an apparatus. In order to avoid vibration resulting from non-concentricity, correction for concentricity has to be performed before using. Usually, a correction point 15 is made by means of drilling a hole at the two ends 11 respectively for the roller 10 rotating with the spindle 14 concentrically.
However, there are following disadvantages while machining the preceding roller 10:
1. The journal 12 at the two ends 11 has to be machined individually such that twice works for clamping and unloading the roller 10 have to be done during machining.
2. Due to twice works for machining the journal 12 at the two ends 11 being done, it is time wasting and it is not easy to control precision of the coaxial line such that defective rate is high.
3. It is easy to hurt the outer surface of the roller 10 being clamped and unloaded several times.
4. The inner wall of the roller 10 is incapable of being lathe-worked except the two ends 11, it is incapable of obtaining a homogeneous thickness of the roller 10 and correction of concentricity leads to high production cost and difficult work such that experienced professional is required.
5. A sufficient thickness of the blank roller has to be retained for cutting and machining such that costs related to material, delivery and machining are hard to reduce substantially.
6. It is complicated to perform machining for the roller so that speed of machining is slow and more material has to be wasted.
Referring to FIGS. 2 and 3, Taiwanese Patent Application No. 90200678 is illustrated. A plurality of mold tools 20 with the same structure are arranged in a squeezing and forming machine and each of the mold tools 20 has a circular surface 23 at the center of the inner wall surface thereof. The diameter of the circular surface 23 is in accordance with the largest diameter of the roller. Both end sections of the respective mold tool 20 has a conical surface 22 next to the circular surface 23 and a concentric circular surface 22 respectively. Hence, when a steel pipe is inserted into the squeezing and forming machine for being formed as a finished roller 30, a conical surface 31 and a concentric journal part 32 at both ends thereof are made in accordance with the conical surface 22 and the concentric circular surface 21 at the same time. In this way, the roller 30 provides the identical concentricity at the outer surface and inner wall surface.
Further, a bearing 32 fits with the concentric journal part 32, which has been finished the surface thereof, so that the axial lines of the spindle 34 and the roller 30 coincide with each other to ensure the concentricity thereof.
The preceding prior art is capable of making the roller 30 with accurate concentricity of the outer and inner wall surfaces to overcome the deficiency of conventional way shown in FIG. 1.